1. The Field of the Invention
The present invention relates to a four-stage phase demodulation low frequency wireless mouse device which divides signals received at a receiving end into four sets of signals having phase information to achieve a preferable noise immunity and increase the reaction speed after being filtered and detected by a low pass filter and a detecting circuit respectively.
2. Description of the Related Art
The present input devices for a computer are divided into a keyboard, a mouse, a trackball, a digital pad, a touch pad and other devices. Due to the increasing use of WINDOW systems in computers, an input device, such as a mouse or a trackball or the like, has become a necessarily fundamental piece of equipment. As to the implementation of a mouse, as a conventional wireline mouse is encumbered with a cable which causes a problem that the mouse can not be dexterously operated, a so-called wireless mouse has become very popular. The way of propagating the signals of the wireless mouse is categorized into two types, one is infrared and the other is ultraviolet. The corresponding relation between the wireless mouse and a receiving device should be a straight line so that an infrared ray can be normally operated since the infrared ray is a linear wave and thus, the infrared wireless mouse is very practical in its physical application and the wireless mouse using a radio transmission method forms a design with less constraints. However, the radio transmission method has its inherent limitation, that is, the radio transmission method is easily interfered with by electromagnetic waves outside which causes a misoperation problem. The electromagnetic interference phenomenon on a computer screen is one example of interference in the radio transmission method since the carrier frequency of a low frequency wireless mouse device is about 100 KHz and the second harmonic (64 KHz to 128 KHz) of a horizontal frequency (32 KHz to 64 KHz) of the computer screen is coincided with the aforesaid carrier frequency. To solve the wireless mouse can only be achieved by raising the mouse immune ability of a wireless receiving device itself.
Taiwan Patent Application No. 79107306, now Taiwan Patent No. 149253 entitled "Wireless Computer Mouse", discloses a quadrature demodulation structure installed on a signal receiving end. As shown in FIG. 3, a radio signal is sent out from a wireless mouse through an AND gate 91, an amplifier 92 and an LC resonant network 93 and the signal is received by an LC parallel resonant network 94 of the signal receiving end. After two mutually inverted signals are generated as the received signal passing through a positive-phase amplifier and a negative-phase amplifier, two sets of signals having a respective phase of 0.degree. and 90.degree. are generated by two electronic switches 971, 972 in which the opening and closing of the two electronic switches 971, 972 are respectively controlled by two sets of timing signals each having a respectively phase of 0.degree. and 90.degree.. Then, the two signals with a phase difference of 90.degree. are combined to form data of mouse (DATA) at an adder 99 after passing through two low pass filters 973, 974 and two amplifiers 981, 982.
Even though the above-described phase demodulation method can decrease tile noise signals, the filtering effect by merely dividing signals into two sets of quadrature amplitude signals still needs to be improved. Furthermore, the reaction speed of the signals can not be increased due to the limitation of noise eliminating ability. Therefore, some problems still remain unsolved.